Titanium rod forging materials are mainly pure titanium and titanium alloy with various components. The original state of materials includes titanium rod, ingot, metal powder and liquid metal. The ratio of the cross-sectional area of the metal before deformation to the cross-sectional area after deformation is called the forging ratio. Proper selection of forging ratio, reasonable heating temperature and holding time, reasonable initial forging temperature and final forging temperature, reasonable deformation amount and deformation speed are very important to improve product quality and reduce cost. General medium and small forgings use round or square bar material as blank. The grain structure and mechanical properties of the bar are uniform and good, the shape and size are accurate, and the surface quality is good, which is easy to organize the mass production. As long as the heating temperature and deformation conditions are properly controlled, the forging with good performance can be produced without large forging deformation. In aircraft, titanium alloy is mainly used to make main stress components such as girders, landing gear, propeller hubs and joints. In the engine, titanium alloy is mainly used to make the conversion ring, the turbine fan, the compressor disc and the blade of the heat stress parts.
Titanium alloy is very sensitive to forging process parameters, and the change of forging temperature, deformation, deformation and cooling rate will cause the change of microstructure and properties of titanium alloy. In order to better control the microstructure and properties of forgings, advanced forging techniques such as hot die forging and isothermal forging have been widely used in forging titanium alloys in recent years. In the conventional forging process, titanium alloys are generally equiaxed, resulting in high room temperature formability and strength. It provides a feasible method to solve the forming of large and complex titanium bar precision forgings. This method has been widely used in titanium rod production. One of the effective ways to improve the fluidity of titanium rod and reduce the deformation resistance Z is to increase the preheating temperature of die. Isothermal die forging and hot die forging developed at home and abroad in the past 20 or 30 years.
In order to improve the yield of titanium rod production, the closed die forging method can be used to die forge titanium rod. The closed die forging method must strictly limit the volume of the original blank, which makes the material preparation process complicated. Whether to use closed die forging should consider both profit and process feasibility. Then only heat treatment and cutting of the Z - end blank. The forging temperature and deformation degree are the basic factors that determine the microstructure and properties of the alloy. The heat treatment of titanium rods is different from that of steel, and die forging is usually used to produce scrap products in shape and size. It has no decisive effect on the microstructure of the alloy. Therefore, the process specification of titanium rod Z post work step has a particularly important role. It is necessary to make the overall deformation of the blank not less than 30% and the deformation temperature not exceed the phase change temperature. In order to make the titanium rod obtain high strength and plasticity at the same time, the temperature and deformation degree should be distributed uniformly in the whole deformed blank as far as possible.
After recrystallization heat treatment, the uniformity of titanium rods and properties is less than that of steel forgings. The low power is fuzzy crystal and the high power is equiaxed fine crystal. Difficult to deform area, because the deformation amount is small or no deformation, its organization is often preserved before the deformation state. Therefore, in the die forging of some important titanium rod parts (such as compressor disc, blade, etc.), in addition to controlling the deformation temperature below TB and the appropriate deformation level, it is very important to control the organization of the raw blank. Otherwise, the coarse crystal structure or some defects will be inherited to the forging, and the subsequent thermal treatment can not be eliminated, which will lead to the scrap of the forging.
When the heat effect is locally concentrated in the area of sharp deformation, the hammer die forging of titanium rod with complex shape. Even if the heating temperature is strictly controlled, the temperature of the metal may still exceed the TB of the alloy. For example, when the blank of the titanium rod with I-shaped cross section is in die forging, the hammer is too heavy, and the local temperature in the middle (web area) is about 100℃ higher than the local temperature at the edge due to the thermal effect of deformation. In addition, coarse-grained structures with low plasticity and durability are easy to be formed in the region with difficult deformation and critical deformation level after die forging. Therefore, the mechanical properties of the forgings with complex appearance are often very unstable. But it will lead to a sharp increase in deformation resistance, although reducing the die forging heating temperature can eliminate the risk of local overheating of the blank. Increased tool wear and power consumption necessitate the use of more powerful equipment. In open die forging, the raw edge loss accounts for 15%-20% of the weight of the blank. The processing waste of the clamping part (if this part must be left according to the die forging conditions) accounts for 10% of the weight of the blank. The relative loss of the raw edge metal usually increases with the reduction of the weight of the blank. Although there is no loss of raw edge in closed die forging, the blank making process is complicated and more transition grooves need to be added, which will undoubtedly increase the auxiliary cost.